The present invention relates to a semiconductor device, a semiconductor module and a hard disk, and especially to a structure capable of efficiently dissipating heat from a semiconductor chip.
Due to the recent growth of the use of semiconductor devices in portable devices and small/densely-mounted devices, the reduction in size and weight and the improvement in heat dissipation properties are demanded at the same time. In addition, semiconductor devices are mounted on various types of substrates, which, in turn, are mounted in various many systems as semiconductor modules. As for such a substrate, the use of a ceramic substrate, a printed board, a flexible sheet, a metal substrate or a glass substrate etc. may be contemplated, and the following description gives one example thereof. Here, the semiconductor module is explained as being mounted on a flexible sheet.
FIG. 17 shows an example in which a semiconductor module using a flexible sheet is mounted in a hard disk 100. This hard disk 100 may be, for example, the one described in detail in an article of Nikkei Electronics (No. 691, Jun. 16, 1997, p.92-).
This hard disk 100 is accommodated within a casing 101 made of a metal, and comprises a plurality of recording disks 102 that are integrally attached to a spindle motor 103. Over the surfaces of individual recording disks 102, magnetic heads 104 are respectively disposed each with a very small clearance. These magnetic heads 104 are attached at the tips of suspensions 106 which are affixed to the ends of respective arms 105. A magnetic head 104, a suspension 106 and an arm 105 together form one integral body and this integral body is attached to an actuator 107.
the magnetic heads 104 must be electrically connected with a read/write amplifying IC 108 in order to perform read and write operations. Accordingly, a semiconductor module comprising this read/write amplifying IC 108 mounted on a flexible sheet 109 is used, and the wirings provided on this flexible sheet 109 are electrically connected, ultimately, to the magnetic heads 104. This semiconductor module 110 is called “flexible circuit assembly”, typically abbreviated as “FCA”.
From the back surface of the casing 101, connectors 111 provided on the semiconductor module 110 are exposed, and these connector (male or female) 111 and connectors (female or male) attached on a main board 112 are engaged. On this main board 112, wirings are provided, and driving ICs for the spindle motor 103, a buffer memory and other ICs for a driving, such as ASIC, are mounted.
The recording disk 102 spins at, for example, 4500 rpm via the spindle motor 103, and the actuator 107 detects the position of the magnetic head 104. Since this spinning mechanism is enclosed by a cover provided over the casing 101, there is no way to completely prevent the accumulation of heat, resulting in the temperature rise in the read/write amplifying IC 108. Therefore, the read/write amplifying IC 108 is attached to the actuator 107 or the casing 101 etc. at a location having a better heat conduction property than elsewhere. Further, since revolutions of the spindle motor 103 tend to high speed such as 5400, 7200 and 10000 rpm, this heat dissipation has more importance.
In order to provide further detail of the FCA explained above, the structure thereof is shown in FIG. 18. FIG. 18A is the plan view, and FIG. 18B is a cross-sectional view taken along the line A—A which cuts across the read/write amplifying IC 108 provided on one end of the module. This FCA 110 is attached to an internal portion of the casing 101 in a folded-state, so that it employs a first flexible sheet 109 have a two-dimensional shape that can easily be folded.
On the left end of this FCA 110, the connectors 111 are attached, forming a first connection section 120. First wirings 121 electrically connected to these connectors 111 are adhered on the first flexible sheet 109, and they extend all the way to the right end. The first wirings 121 are then electrically connected to the read/write amplifying IC 108. Leads 122 of the read/write amplifying IC 108 to be connected to the magnetic heads 104 are connected with second wirings 123 which, in turn, are electrically connected to third wirings 126 on a second flexible sheet 124 provided over the arm 105 and suspension 106. That is, the right end of the first flexible sheet 109 forms a second connection section 127 at which the first flexible sheet 109 is connected to the second flexible sheet 124. Alternatively, the first flexible sheet 109 and the second flexible sheet 124 may be integrally formed. In this case, the second wirings 123 and the third wirings 126 are provided integrally.
On the back surface of the first flexible sheet 109 on which the read/write amplifying IC 108 is to be provided, a supporting member 128 is disposed. As for this supporting member 128, a ceramic substrate or an Al substrate may be used. The read/write amplifying IC 108 is thermally coupled with a metal that is exposed to inside of the casing 101 through this supporting member 128, so that the heat generated in the read/write amplifying IC 108 can be externally released.
With reference to FIG. 18B, a connecting structure between the read/write amplifying IC 108 and the first flexible sheet 109 will now be explained.
This flexible sheet 109 is constituted by laminating, from the bottom, a first polyimide sheet 130 (first PI sheet), a first adhesion layer 131, a conductive pattern 132, a second adhesion layer 133 and a second polyimide sheet 134 (second PI sheet), so that the conductive pattern 132 is sandwiched between the first and second PI sheets 130 and 134.
In order to connect the read/write amplifying IC 108, a portion of the second PI sheet 134 and the second adhesion layer 133 are eliminated at the connection section to form an opening 135 which exposes the conductive pattern 132. The read/write amplifying IC 108 is electrically connected thereto through leads 122 as shown in the figure.
The semiconductor device packaged by an insulating resin 136 as shown in FIG. 18B has heat dissipating paths indicated by arrows for externally dissipating its heat. Especially, since the insulating resin 136 gives the thermal resistance, the semiconductor device has a structure that the heat generated by the read/write amplifying IC 108 cannot be efficiently dissipated to the outside the device.
Further details will now be explained using this example in hard disk application. As for the read/write transfer rate of a hard disk, a frequency of 500 MHz to 1 GHz, or even a greater frequency, is required, so that the read/write speed of the read/write amplifying IC 108 must be fast. To this end, the paths of the wirings on the flexible sheet that are connected to the read/write amplifying IC 108 has to be shorten, and the temperature rise in the read/write amplifying IC 108 must be suppressed.
Especially, since the recording disks 102 are spinning at a high speed, and the casing 101 and the lid provide a molded space, the interior temperature would rise up to around 70 to 80° C. On the other hand, a typical allowable temperature for the operation of an IC is approximately 125° C. This means that, from the interior temperature of 80° C., a further temperature rise by approximately 45° C. is permissible for the read/write amplifying IC 108. However, where the thermal resistance of the semiconductor device itself and FCA is large, this allowable operation temperature can easily be exceeded, thereby disabling the device to provide its actual performance level. Accordingly, a semiconductor device and FCA having superior heat dissipating properties are being demanded.
Furthermore, since the operation frequency is expected to further increase in the future, further temperature rise is also expected in the read/write amplifying IC 108 itself due to the heat generated by computing operations. At room temperature, the IC can provide the performance at its intended operation frequency, however, where it is placed inside of a hard disk, its operation frequency has to be reduced in order to restrain the temperature rise.
As described above, further heat dissipating properties of semiconductor device, semiconductor module (FCA) are demanded in connection with the increase of the operation frequency in the future.
On the other hand, the actuator 107, and the arms 105, suspensions 106 and magnetic heads 104 attached thereto has to be designed as light-weighted as possible in order to reduce the moment of inertia. Especially, where the read/write amplifying IC 108 is mounted on the surface of the actuator 107 as shown in FIG. 17, the weight reduction is demanded also for the IC 108 and FCA 110.